An interesting question to which there is no straightforward answer! For example, in the 1920s many AC bodies were made by specialist coachbuilders, and in the 1930s even in-house made cars were bespoke. So, there were hardly 2 cars alike. Furthermore, right up to the 3000ME there was rarely more than one prototype of a new model, and they were often quite different to the production model. So, where does one draw the line?
The following are some examples of one-off A-Cs in the period 1904 to 1986: Auto-Carrier Ambulance;1913 & 1919 Cyclecars (Archive article to come soon); 1921-26 Race & record cars (at least 6 variants, only 1 survives - Archive article in research); 1932 4-door saloon; 1932 4-seater open sports; 1938 Special FHC (HAS Fry's car); 1946 Two-Litre Hack; 1947 Two-Litre Prototype; 1951 Buckland Special Body; 1953 Two-Litre Coupe; 1953 Ace Prototype; 1954 Ace Flat-4; 1955 5-Seater Flat-4 Experimental; 1958 Ace-Zagato; 1961 Ace-Bristol BEX 1192; 1959 Greyhound Prototypes (2 different bodies); 1962 Greyhound Flat-6; 1963 Greyhound Ford 2.6;1963 Aceca A83; 1963 MA200; Numerous 1960s Cobra 1-offs including A98; 1966 AC427 Convertible; 1971 AC Town Car 3-wheeler and 4-wheeler;1982 AC428 'Mk2'; Frua 7-Litre 4-seater; Numerous 3000ME variants including AC-Ghia, Ghia Quicksilver, 3000ME Lightweight, and '2800ME';1986 'Ace of Spades'.No doubt there are others too!
There are photos of many of these cars in the 60th Anniversary Booklet, and some are featured in past Archive articles.